Yeah, so called advanced civilzation? PAH! they couldn't even come up with metals that don't rust away.

[poor attempt at humour and other pointless nonsense]....[/poor attempt at humour and other pointless nonsense]

Yes, the spacemen kindly brushed all the laptops and laser guns into the ocean because they didn't want the future people to know they existed, for some bizarre reason. Just like God plants fake dinosaur bones to test us.

During the last few decades, we see a shift towards biodegradable materials and recycling. A highly advanced civilisation in the past could have made the same choices and gone beyond. All we have to judge their level of civilisation are a bunch of anarchronistic technological anomalies scattered throughout the world among later civilisations (eg. evidence of travel between the Americas and respectively Europe and Africa prior to Columbus, incredible astronomical knowledge among primitive African tribes or Mayans, incredible accuracy when moving giant stone monoliths, aluminum objects of 3000 years old, etc.).